VLA Test/Observation Coordination Meeting B.G. Clark April 17, 2003 1. eVLA Antenna 13 is now in the Antenna Assembly Building for its mechanical retrofit as an eVLA antenna. It will come out in June, and the eVLA electronics installation will start. As soon as the electronics start to function, various sorts of tests may be run, many of which require work from the scientific staff. B. Clark presented a selection of tasks, which is attached as an appendix below. The workload for the scientific staff appears that it will ramp up through the last quarter of this year, and the need for work will be quite high this winter, through the first quarter of 2004. 2. New correlator controller K. Sowinski indicates that he will drop the capabilities for data selection and for autocorrelation bandpass normalization. He will retain the capability of doing Hanning smoothing. The tentative plan for "channel zero" is to let it be the natural result of the FFT, with the previous functions of "channel zero" being done in other ways. 3. Holography C. Carilli reports that in the recent holography runs, antenna 8 was remeasured. When originally done at Q band in February 2001, it had an RMS of 0.23 mm. Measured in March 2003, it now has an RMS of 0.38 mm. In the interim, the Q band feed was moved around the feed circle to its new location. It appears that the original setting of the surface, in 2001, was correcting for subreflector imperfections as well as those of main reflector. With the feed move, that portion of the surface defects is no longer properly corrected. For best results, the surfaces should be reset yet again after the Q band receiver is moved to its final location. CC feels that the degradation is sufficiently small that this can wait until after antennas have their eVLA upgrade. 4. The antenna 1 saga Antenna 1 was, among other things, initially adjusted at the zenith, unlike all other antennas. It has always behaved differently at high frequencies. K. Sowinski and C. Carilli attempted to sort out the problems. When holography was done in July 2001, the corrections called for at K band and Q band appeared so different that no adjustment of the surface was attempted. Late in 2001, the location of the subreflector was shifted (by quite a lot) in the direction indicated by the coma lobe of the beam at K band. In March this year, holography was done on it, and now the K and Q band patterns agree reasonably, so the surface was adjusted. This has resulted in a factor of order 2 improvement in G/T at Q band, placing the antenna roughly in the middle of the pack. Q band beam cuts done after the adjustment also indicate a reasonable symmetry. It is hoped that the antenna will henceforth act much more nearly the same as all the others. 5. L Band polarization R. Perley says there are now three antennas equipped with the hybrid polarizer which is the current plan for the new eVLA antennas. It is hoped that this will make it possible to more thoroughly evaluate these polarizers. APPENDIX: Plan for tests of eVLA systems. 1. Check for interference, bandpass shapes in 8GHz, 1.5GHz, 350 MHz bands These bands have a bandwidth less than 2 GHz, so the whole band can be examined on a single output of the T304. This should be done in the vertex room, just to be sure it is unaffected by the DTS. Representative spectra recorded with 10 or 20 kHz resolution. Requirements: 8GHz, 1.5 GHz and 350 MHz frontends up and running. T301 converter operating T302 converter working At least one T304 converter working At least one L302 synthesizer working (Perhaps July 2003) Personnel: Frontend group IPG (Minimal scientific oversight) 2. Test of Samplers, DTS, D/As. Repeat of 1 in the control building. Requirements: As for #1, plus At least one D30x At least one DTS receiver board (Perhaps July 2003) Personnel: IPG Data acquisition group (Minimal scientific oversight) 3. Check for interference, bandpass shapes in 45GHz band Repeat of 2 for new 45GHz receiver Requirements: As for #3, plus 45GHz frontend working T303 converter working L301 Synthesizer working and controllable Control of L302 synthesizer August/September 2003 Personnel: Frontend group IPG (Minimal scientific oversight) 4. Check for interference, bandpass shapes in 22GHz band Repeat of 3 for new 22GHz receiver Requirements: As for #2, plus 22GHz frontend working September/October 2003 Personnel: Frontend group IPG (Minimal scientific oversight) 5. Check round trip phase stability Requirements: All 35x modules present and working Monitor data logging from L352 Sometime in July-October 2003 Personnel: LO/IF group (Some scientific oversight) 6. Receiver stability in 8GHz, 22GHz, 45GHz bands 24h+ runs, recording total power, switched power, and the ratio, from the T304 power detectors. Requirements: As for #4, plus Control of noise source switching Monitor data logging from T304 power detectors Perhaps October 2003 Personnel: Frontend Group Scientific Services 7. Tipping curves to evaluate Tcal accuracy and stability Requirements: As for #6, plus Computer control of antenna in az/el coordinates Winter 2003 Personnel: Frontend Group Scientific Services 8. Tipping curves at 1.5GHz to evaluate spillover with new feed Requirements: As for #7 Personnel: Scientific Services 9. Rough single dish pointing (is pointing model working?) Requirements: As for #7, plus Computer control of antenna in ra/dec coordinates Winter 2003 Personnel: Computer Group Scientific Services 10. First fringes Requirements: As for #9, #4, connection to T5's Late 2003 Personnel: Computer Group Scientific Services 11. Evaluation of phase stability compared to VLA antennas Requirements: Software for application of RT phase to correlator data. Late 2003 Personnel: Scientific Services 12. Evaluation of polarization, polarization stability Requirements: As for #11 Personnel: Scientific Services 13. Checkout of new 6 GHz receiver Requirements: Working 6 GHz frontend Late 2003 Personnel: Frontend Group Scientific Services Requirements: As for #7